In the field of medical care, there exist many devices to aid physicians and patients in monitoring a wide range of analyte concentrations related to the patient's body. Such concentrations can for instance be used to monitor if a medical condition is properly controlled by administered drugs, or to aid in reaching a diagnosis of a medical condition from which the patient may be suffering.
Examples of such devices include sensor devices that may be brought into contact with a bodily fluid such as blood or urine, and sensor devices that determine the concentration of a chemical agent in breath expelled by a monitored subject. The sensing functionality of such devices may be provided by dedicated semiconductor devices such as a chemically modified field effect transistor (ChemFET), in which the current characteristics of the transistor are correlated to the concentration of a target analyte.
Well-known examples of such semiconductor devices include transistors covered by a selective membrane such that the transistor would only be exposed to analytes capable of passing the membrane barrier. However, such devices can require complex manufacturing processes, which make them costly.
Some analytes occur in the monitored medium in minute concentrations only, such that accurate detection of these analytes is quite challenging. An example of such an analyte is nitric oxide (NO), which can occur in exhaled breath of human patients and is, amongst others, an indicator of the presence of an inflammation in the lungs of the patient. For this reason, breath analyzers capable of accurately determining the NO concentration in expelled breath are important tools in the treatment of respiratory diseases such as asthma.
US patent application US 2007/0048180 discloses a breath analyzer comprising a nanoelectric sensor capable of determining NO concentrations in the parts-per-million (ppm) range. The nanoelectric sensor comprises a substrate over which one or more nanostructures are disposed. The nanostructures are electrically connected to one or more conducting elements and a recognition material is operatively associated with the nanostructures for interacting with analytes of interest. This document teaches that examples of such a recognition material include metal complexes of porphyrins and phthalocyanins, as well as conductive polymers such as polyaniline and polypyrrole.
A drawback of this breath analyzer is that the sensitivity of the nanoelectric sensor to NO does not extend to the parts-per-billion (ppb) range, which is the typical concentration range of NO in human breath. Consequently, the usefulness of this breath analyzer for the purpose of detecting NO in exhaled human breath is limited. In addition, the use of nanostructures as channel material means that standard manufacturing processes for manufacturing semiconductor devices cannot be used, which adds to the cost of both the nanoelectric sensor and the breath analyzer.